No, drinking caffeinated or sparkling soft drinks does not weaken your bones or cause osteoporosis. For more than fifteen years, a series of credible scientific organisations have studied whether the phosphorus and/or caffeine in sparkling drinks has any impact on bone health and found that there is no negative effect in healthy individuals as long as their calcium intake is sufficient. Risk factors for osteoporosis listed by the International Osteoporosis Foundation include age, female gender, family history, menopause, poor nutrition, insufficient calcium and vitamin D intakes, insufficient exercise, low body mass index (being too thin), smoking and excessive alcohol consumption.
Phosphoric acid contains phosphorous which is actually an essential nutrient. Coca‑Cola contains phosphoric acid as it is this ingredient that gives the drink its tangy Cola taste. The amount of phosphorous in Coca‑Cola is very small compared to many other foods.